This invention relates to an air-fuel ratio controlling device for internal combustion engines, and more particularly to an air-fuel ratio controlling device for internal combustion engines, which is adapted to detect the combustion condition in a cylinder, feed back a signal representative of the mentioned combustion condition, and control in accordance with the signal an air-fuel ratio in a gaseous mixture to be supplied to the cylinder.
In a conventional air-fuel ratio controlling device for internal combustion engines, a zirconia-oxygen sensor is widely used as an air-fuel ratio sensor. An output signal from this sensor is fed back to control a ratio of the air to fuel (air-fuel ratio) in a gaseous mixture, which is supplied to a cylinder in an internal combustion engine through a carburetor or a fuel injector, in such a manner that the air-fuel ratio is kept close to a theoretical value. This zirconia-oxygen sensor is provided in an exhaust pipe-gathering section, or a section on the downstream side of the exhaust pipe-gathering section, of the internal combustion engine, and adapted to detect a concentration of the oxygen in an exhaust gas, which occurs after the gaseous mixture is burnt, and thereby determine the suitableness of the air-fuel gaseous mixture. However, since the gaseous mixture, an air-fuel ratio in which is to be controlled, flows in a passage extending from the cylinder to the exhaust pipe, the response time for the controlling of an air fuel ratio becomes long. Accordingly, it is very difficult to control an air-fuel ratio accurately, especially, when a load is changed suddenly.
The zirconia-oxygen sensor is not sufficiently operated at a low temperature, so that it cannot be used to control an air-fuel ratio when starting an engine. Moreover, an output from the zirconia-oxygen sensor greatly varies with respect to a special air-fuel ratio (for example, a theoretical air-fuel ratio) but it is difficult to obtain such outputs therefrom that vary linearly in their levels with respect to air-fuel ratios in a wide range.